A centrifugal pump for the forced transfer of liquids generally includes a spiral-shaped housing within which an impeller having a plurality of blades operatively rotates. The impeller is mounted on a shaft that is supportedly carried on bearings disposed about the shaft. As a consequence of the spiral shape of the housing, the distance between the impeller shaft and the outer or peripheral wall of the housing varies continuously as the impeller operatively rotates, thus producing a radial force on the impeller. These radial forces are transferred to the pump shaft and carried by the bearings. Such pumps are designed to maximize their operating efficiency, and to minimize the radial forces on the impeller, at or under certain predefined working or operating conditions. A pump's characteristic curve defines the relationship between the pump's lifting height and the volumetric liquid flow through the pump at a given pump impeller rotation speed, and may be employed--if the then-current or instantaneous operating point along the curve is accurately determinable--to facilitate efficient operation of the pump.
The use of heretofore known devices for determining a pump's current operating conditions and identifying the point along the pump's characteristic curve at which it is operating requires that the pump incorporate two liquid outlets for measuring the pressure at or adjacent the pump. In addition to the practical and technical drawbacks and other implications of such a design, the resulting measurements are comparatively unreliable as an indicator of the pump's then-current operating condition. A precise determination of the actual current operating point of the pump along its characteristic curve is important where, for example, the pump forms a part of a processing stage or apparatus and is controllable, using or on the basis of reliably-measured values, to maximize its efficient operation in the process.
Using the method of the present invention the magnitude and direction of the radial forces imposed on the pump or impeller shaft are measured with great precision. These values are then compared with previously-measured or determined or otherwise known values to accurately identify the actual point along the pump characteristic curve at which the pump is operating.